Isomerization of hexane



S ept. 22, 1959 D. H. BELDEN IsoMERIzATIoN oF HEXANE Filed Aug. 2, 1957xtmnxm 25N ankommt Enns@ mmh QQ 83am@ MDS Babs@ N VEN TOR.' Dona/d H.Belden A TTORNE YS.

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N Zh um United aStates Patent" C) ISOMERIZTION 0F Donald H. Belden,Prospect Heights, Ill., assiguor, by

mesne assignments, to Universal Oil Products Company, Des Plaines, lll.,a corporation of Delaware Application August 2,1951, Serial No. 675,882f 6 Claims. (Cl. 26o-683.68)

butanes and pentanes in which process high yields` of two separate highantiknock hydrocarbon fractions are. produced. This invention alsorelates to a particularl series of process steps, the Vuse of whichresults .in maximum catalyst life and optimum product quality; Theseob'- jectives are accomplished by the 'uniqueI combinationv processv ofthe present invention as will be set forthhereinafter.

Production of highly branched chain paraffin hydrocarbons having' high'yantilrnock properties and therefore suitable for use in automotiveand'aviation fuels: is of considerable importance in the petroleumrefining industry. Furthermore, the recent introduction of automobileengines of high compression ratio has necessitated the* utilization ofhigh antiknoclc fuels, iny these. engines to obtain maximum horsepoweroutput therefrom. Til-us the demand for higher and higher octane. numberfuels has led to-the need for increased quantities of highly branchedchain paraiinic hydrocarbons of high antiknock values.-

A: convenient source of such highly branched chain parafnic hydrocarbonsis the catalytic isomerization of less highly branched'chainparailinicihydrocarbons. Normal butano and normal pentane havebeen'isomerized to' iso butane and isopentane, respectively,by variousprior art processes` utilizing either liquid orvapor phase.. How-1 ever,it iswell known in the art thatA crackin-g occurs along withisomerizatiorn and that this. cracking increases with increasingmolecular weight of the hydrocarbonreactant. A process of theisomerization of hexane is therefore particularly attractive when it isrealized that thev hexane fraction can be converted by properisomerization and fractionation into a high antiknock hydrocarbonfraction. It is therefore an objective of this invention toV providesuch a-` process which will yield thesedesired high octane hexaneisomers.

Prior art processes forthe isomerization of vsaturated hydrocarbons havetaught ther-use of various catalytic agents to accelerate the desiredmolecular rearrangement.

at the particular operating conditions selected. Various catalyticagents which have been utilized are. metal halides such as aluminumchloride, aluminum bromide, etc.,- and these catalytic agents wereactivated by the Vaddition of their respective hydrogen halide. Becausethese catalytic agents have a very high activity factor, variousdisadvan-v tages resulted with the use of these agentsv inthe isom-`erization of a hexane fraction. One of-thedisadvantages is the fact thatthese catalytic agents notV only ac celerate isomerization reactions,but they also accelerate ICC eraclri'ngy or decomposition reactions.These decomposition reactions are particularly detrimental to theoverall economics of an isomerization process since they cause the lossof a portion of the charging stock as well as in-l butane,2-methylpentane, B-methylpentane, n-hexane,`

methylcyclopentane, benzene, and cyclohexane. Thefboil-v ing range ofsuch a hexane fraction is from about F. to about F. By the combinationprocess of this invention the high octane number components are selec'-tively fractionated so that only a minimum of these components arepassed to the isomerization reaction zone. The isomerization reactionzone feed will be a fractioncomprising Z-methylpentane, B-mcthylpentane,normal hexane, and some methylcyclopentane. This isomeriza` tionreaction zone feed will be converted to an equilibV` rium mixture ofhexane isomers which will comprise 2,2-v dimethylbutane',2,3-dimethylbutane, Z-methylp'entane, 3- methylpentane, normal hexane,methylcyclopentane, and cyclohexane. By lthis particular-process andselective fractionation therein, two high octane number hydrocarbonproducts are attained, both productsI of higher octane number than thefresh feed.

One embodiment of this invention provides a process for theisomerization of an isomerizable saturated hydro carbon fraction in thepresence of hydrogen and an isom# erization catalyst which comprisesintroducing a saturated hydrocarbon fraction into an intermediatesectionY of a rst fractionation zone while at the same time passing avportion of a liquid phase product stream from the bottom of a secondfractionation zone to the upper por.- tion ofV said first fractionationzone, passing a vapor phase saturated hydrocarbon fraction from an upperportion of said first fractionation zone to the lower portion of saidsecond fractionation zone, removing from the bottom of said firstfractionation zone an isomerization reaction'.

zone feed and introducing said feed into an isomerization reaction zonewherein low octane number saturated hydrocarbons are isomerized tohigher octane number saturated hydrocarbons, passing a liquid phaseeluent stream v from said isomerization reaction into anntcrmediate.portion of a second fractionation zone, removing overhead from saidsecond fractionation zone a high octane number product enriched inisomerized hydrocarbons, passing from the bottom of said secondfractionation zone a second product which is partially enriched inisomerized hydrocarbons and returning a portion of said second productto the upper portion of said first fractionation zone as aforesaid.

Another embodiment of the present invention providesy drawing from thebottom of said first fractionation zone a hydrocarbon fraction enrichedin normal hexane and passmg said fractlon to an isomerization reactionzone wherein said fraction is contacted with hydrogen and saidisomerization catalyst at isomerization conditions toI produce anenriched isohexane effluent fraction, introducing said isomerizationeffluent into an intermediate portion of a second fractionation zone,passing overhead from said second fractionation zone an isohexaneenriched high octane number hydrocarbon fraction, with drawing from thebottom of said second fractionation zone a lower octane number productthan the overhead product, and passing a portion of said product to theupper portion of said first fractionation zone as aforesaid.

The process of the present invention has several advantages, allinterrelated. One of the advantages contained in the present process ofthis invention results from the particular arrangement of the selectivefractionation section of the process. As stated hereinabove, the hexanefractions which are suitable for use as feed stocksA in the process ofthe present invention contain various hexane isomers and cycliccompounds. To produce satisfactory octane number products by theisomerization process of this invention it is necessary that a maximumamount of isomerization of the lowest octane number isomer, normalhexane, be accomplished. Another hexane isomer which occurs in thesefeed stocks is methylcyclopentane. This isomer has a boiling point of161, while normal hexane boils at 156 F. From these two boiling pointsit is obvious that fractionation of one of these components from theother presents a difficult problem. In isomerization of hexane fractionsa portion of the cyclics contained in the fresh feed is converted tonon-cyclic components. The reaction zone feed must be a bottomsfraction, since Water or its oxygen equivalent, which is found in thefresh feed must be removed overhead by distillation drying since thepresence of water in the reaction zone feed would tend to deactivate theisomerization catalyst. However, it is obvious that cyclic componentswill tend to build up in the reaction zone feed because of the higherboiling points of the cyclic compounds. In the process of the presentinvention where it is desired to produce two higher octane numberproducts from one lower octane number feed stock. it has been found thatcyclics build up in the reaction zone feed can be prevented byintroducing the isomerization reaction'zone effluent product at anintermediate point in a fractionation zone between the withdrawal pointsof the two desired higher octane number products. This is contrary towhat is taught in the prior art where recycle is combined with freshfeed for introduction into a fractionation zone. A critical feature ofthe process of the present invention is that the reaction zone liquideffluent is introduced at an intermediate point between the withdrawalpoints for both liquid products. By the introduction of the effluentstream at this intermediate point the quantity of cyclics in theisomerization reaction zone feed will be maintained constant since aportion of the cyclics equivalent to that introduced in the fresh feedwill be drawn off at the withdrawal point of the intermediate octanenumber liquid product. lf the reaction zone effluent is introduced tothe fractionation zone of the present process at a lower point than thewithdrawal point for the intermediate octane number product, cyclicbuild up will occur in the process. By varying the point of introductionof the reaction zone efliuent into the intermediate portion of thefractionation zone, one can vary the octane number of the products toattain that which is desired. Another advantage of the process of thepresent invention is that catalyst deactivation or destruction isminimized or substantially eliminated by distillation drying of thereactor feed and rejection of small amounts of water contained thereinalong with the dirnethylbutanes in the overhead from the rstfractionation zone. All isomerization catalysts depend upon an acidfunction to accomplish the desired isomerization reaction. This acidfunction is destroyed or decreased by the contact of the catalyst withwater. Utilization of the process of the present invention prevents thisdeactivation. A further advantage of the process of this invention isthat by the elimination of dimethylbutanes, from the reaction zone feed,the quantity of reaction zone feed is reduced as well as the combinedfeed ratio and thus the total investment necessary for catalyst can besubstantially reduced. Theseand other advantages will be explained morefully in the following detailed descrip- Y- tion of the process of thepresent invention.

As set forth hereinabove this invention relates to a. process for theisomerization of paraflinic hydrocarbons boiling above butanes andpentanes. Hydrocarbons within the scope of the above limitation andutilizable in the process of this invention include methylcyclopentane,

cyclohexane, normal hexane, Z-methylpentane, S-methylpentane,2-methylhexane, 3rnethy1hexane, S-ethylpentane, n-heptane,methylcyclohexane, ethylcyclohexane, noctane, Z-methylheptane,B-methylheptane, etc. The

j process of this invention is particularly applicable to the .Lcomponent.

isomerization of hexane fractions. Various sources of these hexanefractions include fractionation from straight run gasoline, straight runnaphtha, natural gasoline, catalytically reformed naphtha, andcatalytically reformed gasoline.

Isomerization catalysts which are utilizable within the generally broadscope of the process of the present invention are herein set forth.These catalysts include a support, an acid-acting function, and ahydrogenation The support may be selected from various diverserefractory oxides including silica, alumina, silicaalumina,silica-alumina-magnesia, silica-alumina-zirconia, silica-zirconia, etc.Depending upon the method of preparation and upon the treatment of thesupport thereafter, these various supports will have surface areasrangparticularly gamma-alumina having a surface area of from about 150to about 450 square meters per gram. When gamma-alumina is utilized asthe support, the acid-acting function can be added to the catalyst bythe incorporation therein of what is known in the art as combinedhalogen. The amount of combined halogen can be varied from about 0.01 toabout 8% by weight based on the alumina. 0f the various halogens whichmay be utilized, both iiuorine and chlorine can be used satisfactorily.Thus in an alumina type catalyst to be utilized at reaction temperaturesof from about 750 to about 850 F., about 0.3% by weight of fluorine andabout 0.3% by Weight chlorine may be incorporated therein. When it isdesirable to utilize the catalyst at lower temperatures, for example,about 500 to about 750 F., as in the case in the preferred embodiment ofthe invention, the combined halogen which will be utilized along withthe alumina support is fluorine, and this fluorine will be utilized inan amount of from about 2.5% to about 4.5% by weight. The composite willthen have the desired hydrogenation component combined therewith. Thishydrogenation component willV normally be selected from groups VI(B) andVIII of the periodic table or mixtures thereof. Such hydrogenationcomponents include chromium, molybdenum, tungsten, iron, cobalt, nickel,and the so-called platinum group metals including platinum, palladium,ruthenium, rhodium, osmium, and iridium. Of the various hydrogenationcomponents which may be utilized those of the platinum group metals arepreferred, and of these platinum group metals, platinum itself isparticularly preferred. The hydrogenation component of the catalyst ofthe present invention-will normally be utilized in anv amount-cf from'about 0.01% to about- 10% by weight based fonthe-weight -ofthesupport.With the preferred platinum group metals, particularly platinum, the.quantity;utilized will range from about 0.01% to about 2%. by weight. A.particularly preferred catalyst comprising platinum, combined halogen,and alumina will contain ;4% platinum, 4.0% fluorine, and alumina.Because ofV equilibrium considerations andbecause it is often desirableandor advisable -to carry out the isomerization reaction-at the lowestpossible temperature, for example, from-aboutv 300 toabou-t 500 F.,catalysts may also be prepared by yimpregnatingl composites such-asdeseribed hereinabove with-a metal halide of the Friedel-Crafts typeFor example, an kexcellent low temperatureisomcrit/:ation catalyst canbeV prepared by impregnating from Yabout to vabout 20% aluminum chloride:onto a composite 1 of platinum, alumina, and combined halogen.`'Ille-@process of the presen-t invention lcan -be Aused with other.catalysts but not-necessarily with equivalent results.' SuchcatalystsvareV aluminum chloride sludge, aluminum bromide sludge, etc.,which may be used -along with hydrogen chloride, hydrogen bromide, etc.,if .so desired. VThe:isomerization processof thisinve'ntion may becarriedioutfat varying conditions of temperature, pressure, liquidhourly space velocity, and combined feed lratio. The ternperatureutilized' will .generally be` dictated by the particular isomerizationcatalyst and thereforel tem'- peratureswill be from about..300 F-.itorabout 800 F. 'Ifhepressure selectedfor the isomerization reactionzo'neWillzbelow.- enough: so as.-to insure vapor operation of theisomerization reaction zone feed and this pressure will-range fromlabout 100A pounds Iper' square inch to about: 1000 .poundsper-squarepinch. The `liquid hourly space velo'eity-(which may bedenedas the; ratio of the liquidvolume of inlet material to the volume of thereaetionspace) willrange from about 0.1 to; about l0 ormore, theonlyl-i'mitation :being that equilibrium mixtures fof-isome'rizedhydrocarbons are obtained in the reactionzone "eiuentf. Thecombined-feed ratio (which may be defined as the total amount of freshfeed plus the 1. recycle reaction Yzone effluentfentering thereactordivided by thefquantity'of fresh'feed) will range from aboutl tov about5 or more. In the-preferredembodi-4 ment offthe :present invention,hydrogen is utilized to minimizecracking and to maintain thesurfaceofthe catalyst in a. carbonv free condition. The quantityof hydrogenutilized will range from about 0;25 to about =mols or more of hydrogenper mol of hydrocarbon. The #hydrogen consumption 4will -be exceedinglysmall, inz-'th'egrange of from about l30 to about 100 cubic feetprbarrel ,of hydrocarbon feeds The .process of .the presentinventioncan; perhaps be bestunderstood by reference to the accompanyingdrawing.- whichv is a schematic diagram :ofthe process ow; Referring toVthe .drawing of :Figure I, a saturated hydro'- carbon:;fraction `whichis enriched in normal. hexane is introduced. through line 1 into anintermediate portion Off :fractionation zone- 2. The aforesaidhydrocarbon fraction is -fractionated'in'fractionation zone 2 so'that aportion ofthe branched-chain isomers contained. in the fresh feed may bepassed overheadthrough'line 24. The liquid-.portion of theremaining`hydrocarbon fraction will be-.withdrawn from: the bottom .ofYfractionation. zone 2 through. line V3 and passed on to anisomerization reac= tion zone-1 for subsequent conversion to highloctane number. isomers. A rising vapor stream in fractionation zoneLZispassed 'overhead through line 24 to'the lower poi-tiongof-a secondfractionation zone 12..whereintwo high octane number hydrocarbonyproducts will be with2 drawn from saidffractionation rone .12.Ahydrocarbon fraction substantially rich-in normal hexane is withdrawnfrom-thebottom of fractionationzoneZ bycondit means tandis passed to aheater 4 where a vaporphase isomerization reaction zone feed iswithdrawn by means` ofaconduit andcombined with a'hydrogen gas recyclestream incline 10. -The` hydrogen gas recycle-streamjs supplemented by amake up of hydrogen introduced through line 11. The combinedisomerization reaction zone lfeed and hydrogen recycle gas are passedthrough conduit means 5 into reaction zone 6 wherein isomerizable vaporphase hydrocarbons are converted to high octane number isomers.Isomerization reaction zone efliuent is withdrawn from thebottom ofreaction zone 6 through conduit means 7 and is introduced intoseparation zone V8 wherein a liquid phase hydrocarbon product stream isseparated from a substantially pure hydrogen gas stream: Thesubstantially pure hydrogen gas stream is withdrawn from separation zone8 by means of conduit 10. A liquid hydrocarbon product stream `iswithdrawn from the bottom of separation zone 8 by means of conduit 9 andis introduced into an intermediate portion of fractionation zone 12.

An'alternate flow of the hydrocarbon product stream after discharge fromseparation zone 8 is-illustrated in the drawing of FigureI wherein aconventional debu-l tanizer 28 is shown. This debutanizer isaconventional fractionation zone by means of which a light hydrocarbongas'or low boiling cracked products are removed from the process. Thisremoval is accomplished by the closg ing of valve 26 in line 9 and theopening of valve 27 in line 25 so that the hydrocarbon product streampasses directly from the bottom of separation zone 8 through line 9 andinto the lower portion of debutanizer column 2.8.y The debutanizedproduct is withdrawn from the bottom of column 2S by means of line 29which is joined to line 9 by the opening of valve Y31. The lighthydrocarbon gases arewithdrawn from the top of column 28 by means ofline 30. I

The debutanizer column 2S is eliminated from the ow of theisomerizationreaction zone eifluent by the closing of valve 27 in line25, the closing of valve 31 in line 29,V and the opening of valve 26 inline 9. The efuent stream now flows directly from the bottom ofseparation Y8 through line 9 into an intermediate portion of fractionavtion zone 12. l

The purpose of fractionation zone 12 is to separate by fractionaldistillation the isomerization reaction zone efhuent stream to producetwo separate product streams of high antilrnock hydrocarbons. Theisomerization reaction zone efuent is enriched inbranched-chain isomersfrom the fresh feed that are introduced into fractionation zone 2 whileat the same time unconverted isomerizable hydrocarbons are passed fromthe lower portion of rfractionation zone 12 into the upper portion offractionation zone 2 back to the isomerization reaction zoned... Aconduit 20 is provided from the lower portion of fractionation zone 12for the withdrawal of an intermediate product of a middle octane numberhydrocarbon and cyclic componentswhichare withdrawn by means of line 21.In the drawing, specification, and claims'the withdrawal is shown anddiscussed as a bottoms with.v-` drawal. By the use of the term bottom nointention is meant to restrict the withdrawal to the eX-act bottom ofthefractionation zone but the bottom may refer to.` any lower portion ofthe fractionation zone. A hydro`v carbon fraction containing high octanenumber isomers' is passed overhead from fractionation zone 12 andwithdrawn by means of conduit 13 and introduced into a cooler'lii'frornwhere a liquid product stream passes to receiver 15. The highl octanenumber hydrocarbon prodi uct is withdrawn from receiver 15 by conduit 16and a portion of this product is returned as reflux to fractionationione 12 .by meansof pump 18 and conduit 19.` If .the debutanizer column28 has been eliminated from the process flow of this invention, then thelow boiling hydrocarbon gassesare removed from the process by passingsaid gases from receiver 15- by means of line 33l and pressure.control'valve .34. The remainingrhydro-f carbon, isomerization'reaction` `zone product is :passed: tot

7 line 17 from where it is withdrawn as a high octane number hydrocarbonproduct stream.

Another modification of the invention is shown in Figure II. Thismodification resembles the process of Figure I except that in thisinstance the second fractionation zone 12 is shown superimposed andinternally connected with the first fractionation zone 2, however,separate zones may be utilized within the scope of this improved processas is illustrated in Figure I.

Referring to the drawing of Figure II, a saturated hydrocarbon fractionwhich is enriched in normal hexane is introduced through line 101 intoan intermediate portion of fractionation zone 102. As has previouslybeen stated the aforesaid hydrocarbon fraction 101 is fractionated inthis portion of fractionation zone 102 so that a portion of the branchedchain isomers contained in the fresh feed may be passed to the upperportion of fractionation zone 112. The liquid portion of the remaininghydrocarbon fraction will be withdrawn from the bottom of fractionationzone 102 by means of conduit line 103 and passed on to an isomerizationreaction zone for subsequent conversion to high octane number isomers. Arising vapor stream in fractionation zone 102 is passed to a lowerportion of a second fractionation zone 112 wherein two separate highoctane number product streams are withdrawn from said fractionation zone112. A liquid hydrocarbon stream which has been passed through theisomerization reaction zone is introduced into an intermediate portionof fractionation zone 112 by means of line 109. The purpose offractionation Zone 112 is to separate by fractional distillation theisomerization effluent stream to produce two separate streams of highanti-knock hydrocarbons. The isomerization reaction zone effluent isenriched in isomers from the fresh feed that is introduced intofractionation zone 102 while at the same time the unconvertedisomerizable hydrocarbons are passed from the lower portion offractionation zone 112 into the upper portion of fractionation 102 forsubsequent recycle back to the isomerization reaction zone. Conduit 120is provided from the lower portion of fractionation zone 112 for thewithdrawal of intermediate product of middle octane number hydrocarbonand cyclic components that collect on collecting plate 132 and thus thereturn of these cyclic components to the isomerization reaction zone issubstantially prevented. A hydrocarbon fraction containing high octanenumber isomers is passed overhead from fractionation zone 112 and iswithdrawn by means of conduit 113 and` introduced into a cooler 114 fromwhere a liquid product stream passes to receiver 115. A high octanenumber hydrocarbon product is withdrawn from receiver 115 by conduit 116and a portion of this product is returned as refiux to fractionationzone 112 by means of pump 118 and line 119. The remaining hydrocarbonisomerization reaction zone product is passed to line 117 from where itis withdrawn as a high anti-knock hydrocarbon product. If thedebutanizer column 28 has been eliminated from the process ow of thisinvention, then the low boiling hydrocarbon gases are removed from theprocess by passing said gases from receiver 115 by means of line 133 andpressure control valve 134.

Example I One specific example of the operation of the process of thisinvention in the presence of a catalyst comprising platinum, aluminum,and combined halogen is herewith described.

The process is carried out similar to that set forth hereinabove withreference to Figure i and the catalyst utilized comprises aluminacontaining 0.4% platinum and about 4.5% combined tiuorine.

' This example illustrates the isomerization of a hexane fraction havinga boiling range of from about 30 C. to about 90 C. The composition ofthis hexane fraction is as follows: cyclopentane, 0.8%;2,2-dimethylbutane,

1.7%; 2,3-dimethylbutane, 5.1%; 2-methylpentane', 25.8%;S-methylpentane, 16%; normal hexane, 39.4%; methylcyclopentane, 6.2%;cyclohexane, 2.9%; and nor.- mal heptane, 2.1%. Referring again to thedrawing of Figure I this hexane fraction in the quantity of 432 mols perhour is passed as a liquid through line 1 into an intermediate portionof fractionation zone 2. The aforesaid hexane fraction is fractionatedin this portion of fractionation zone 2 so that a portion of thebranched chain isomers contained in the fresh feed may be passedoverhead. A rising vapor stream in fractionation zone 2 is passed to thelower portion of a second fractionation zone 12 by conduit means 24wherein two separate high octane number products will be withdrawn fromsaid fractionation zone 12. A portion of the isomerization reaction zoneeffluent is withdrawn from the bottom of said fractionation zone 12 bymeans of line 20 and passed to the upperportion of said fractionationzone 2 by means of pump 22 and line 23. This effluent fraction iscombined with fresh feed introduced into fractionation zone 2 for thefurther fractionation of the combined feed so that a.; isomerizationreaction zone feed is prepared which contains an equilibrium quantity ofcyclic components and an increased quantity of isomerizablehydrocarbons.

The isomerization reaction zone feed is withdrawn from the bottom offractionation zone 2 by means of line 3. The isomerization reaction zonefeed is charged at the rate of 480 mols per hour to a heater 4 and thisfeed comprises 9 mols per hour of 2,3-dimethyl butane, 80 mols per hourof Z-methylpentane, 77 mols per hour of 3-methylpcntane, 203 mols perhour of normal hexane, 60 mols per hour of methylcyclopentane, 18 molsper hour of cyclohexane, and 33 mols per hour of normal heptane. Thecornbined feed ratio which has been hereinabove defined is 1.1 in thisparticular example. The aforesaid isomerization reaction zone feed isintroduced into heater 4 and is substantially vaporized therein andwithdrawn from said heater at a temperature of 600 F. The substantiallyvaporized isomerization reaction zone feed is Withdrawn from heater 4through line S at a temperature of 600 F. and is combined with ahydrogen recycle gas stream line 10, the hydrogen recycle gas rate beinghigh enough so that a mol ratio of combined hydrocarbon feed to mols ofhydrogen gas is 2. This is accomplished by recycling the hydrogen fromthe separation zone 8 to the isomerization reaction zone 6. A smallamount of substantially pure make up hydrogen is added to the systemthrough line 11 to compensate for the hydrogen used up in the reactionand that which is removed as dissolved gas. The reaction is carried outat a pressure of 550 pounds per square inch in vapor phase at a liquidhourly space velocity of 2. As set forth hereinabove isomerization ofthe reaction zone feed is accomplished in reaction zone 6 in thepresence of the hereinabove described catalyst and results in theproduction of 480 mols per hour of reaction zone effluent containing 56mols per hour of 2,2-dimethylbutane, 31 mols per hour of 2,3-dimethy1-butane, 121 mols per hour of Z-methylpentane, 82 mols per hour of3-methylpent'ane, 82 mols of normal hexane, 64 mols ofmethylcyclopentane, 10 mols per hour of cyclohexane, and 34 mols ofheptane.

The isomerization reaction zone eiuent is withdrawn from reactor 6 bymeans of line 7 and passed to a separator 8 wherein a separation ofliquid hydrocarbon and recycle hydrogen gas is attained. The hydrogenrecycle gas is passed overhead from separator 8 by means of conduit 10which joins the combined feed to the isomerization reaction zone in line5. The isomerization reaction zone efuent is withdrawn from separator 8by means of conduit 9 and in this particular case is passed to adebutanizer column 28 wherein the low boiling hydrocarbon gases arepassed overhead from said debu-l tanizer column 28 it is necessary thatvalve 26 in line 9 be closed and the valve 25 in line 27 and valve 3,1in line 29 be opened. In this manner a debutanized product-may`benwithdrawn tr'omr-y column28 by meansl of line .129 andVpassedvthrough valve'SI which joins Vsaid debutanized product to line 9.

The isomerization reaction zone eiiiuent is introduced by meansVroff-conduit9 into the intermediate lportion of fractionation zonelZ. ,Aseparation of two high octane number hydrocarbon fractions is maintainedin fractionation zone 12 so-that-the-quantityofhigh octane numberhydrocarbon being passed overhead' from said fractionationczone I2is-149 molsper hour which contains 5'3 mols per hour of2,2-dimethylbutane, 18 mols per hour of 2,3-dimethy1butane, 47 mols perhour of Z-methylpentane, 15 mols per hour of 3-methylpentane, 4 mols perhour of normal hexane, and 2 mols per hour of methylclyclopentane. Thishigh octane number hydrocarbon product is withdrawn from the top offractionation zone 12 by means of conduit 13 and passed to a cooler 14and then to a receiver 15. The product in receiver 15 is then withdrawn`from the bottom by means of conduit 16 and a portion of said highoctane number hydrocarbon is returned as reux by means of pump 1S andconduit 19 to the upper portion of said fractionation zone 12 while theremainder, 149 mols per hour, is withdrawn as high octane numberhydrocarbon product by means of line 17. The particular octane numberobtained in this product stream that is withdrawn by means of line 17 is98 F-l-i-3 cc.

Further fractionation is effected in fractionation zone 12 so that aproduct stream of the quantity of 275 mols per hour is withdrawn fromthe lower portion of fractionation zone 12 by means of conduit line 20.The product stream withdrawn through line 20 contains 8 mols per hour of2,2-dimethylbutane, 23 mols per hour of 2,3-dimethylbutane, 103 mols perhour of 2methyl pentane, 58 mols per hour of S-methylpentane, 48 molsper hour of normal hexane, 27 mols per hour of methylcyclopentane, 3mols per hour of cyclohexane, and 8 mols per hour of normal heptane. Theoctane rating of the aforesaid hydrocarbon fraction in this particularcase is 90 F-1-1-3 cc. A sufficient quantity of the product streamwithdrawn from line 20 is returned by means of pump 22 and line 23 tothe upper portion of fractionation zone 2 so that the combined feedratio of 1.1 is maintained. In addition, however, to maintaining thiscombined feed ratio the particular arrangement of fractionation zone 12and fractionation zone 2 is such that the cyclics rejected from theprocess through line 20 permits the lower boiling isomerizablehydrocarbons to combine with the fresh feed that is introduced throughline 1 into said fractionation zone 2 and thus provide a desirableisomerization reaction zone feed. Without this cyclics rejection thisprocess would be inoperative since the cyclics could build up in theisomerization reaction zone feed to a point where they would simply backout all of the fresh feed.

The particular operating conditions used in fractionation zone 2 aresuch that the bottom temperature of fractionation zone 2 is of the orderof about 250 F. while the top temperature of said fractionation zone 2is of the order of 235 F. The operating conditions maintained infractionation zone 12 are such that the bottom temperature of saidfractionation zone 12 is of the or`der of about 235 F. and the uppertemperature of said fractionation zone 12 is of the order of 190 F.While the pressure maintained on both fractionation zone 2 andfractionation zone 12 is of the order of about 45 pounds per squareinch.

I claim as my invention:

1. A process for the isomerization of an isomerizable saturatedhydrocarbon fraction which comprises introducing said saturatedhydrocarbon fraction into a first fractionation zone while at the sametime passing a liquid phase product stream from the bottom of a secondfractionation zone to the upper portion of said first fractionationzone, passing a vapor phase saturated hydrocarbon 10 fractionffromanuppen portion of .said rstfractionation zone t to the lower?r portionof. Isaid second fractionation zone, .removing :fronti the bottom ofsaid first fractiona-1 tion zonef..-a.n;ison:te1:ization.reaction zonefeed and vintroducing.- said feed into.V an'isomerization reaction;zone*v wherein low octanenum-ber saturatedhydrocarbons are isomerizedto`higher octane knumber saturated `hydrof carbons, passing a `liquidphase'Y efiluent stream from said isomerization reaction'` zone into an`intermediate portion of said. second :fractionation V zone, y.removingoverhead from said second fractionation zone a high octane numberproduct enriched in isomerized hydrocarbons and recovering the same,passing from the bottom of said second fractionation zone a secondproduct which is partially enriched in isomerized hydrocarbons andreturning a portion of said second product to the upper portion of saidfirst fractionation zone as aforesaid and recovering another portionthereof.

2. A process for the isomerization of hexane which comprises introducinga normal hexane liquid stream into an intermediate portion of a firstfractionation zone while at the same time passing a liquid phase productstream from the bottom of a second fractionation zone to the uppersection of said first fractionation zone, passing isohexanes from anupper portion of said first fractionation zone and introducing the sameinto the lower portion of said second fractionation zone, withdrawingfrom the bottom of said first fractionation zone a hydrocarbon fractionenriched in normal hexane and passing said fraction to an isomerizationreaction zone wherein said fraction is contacted with hydrogen and anisomerization catalyst at isomerization conditions to produce anenriched isohexane eiuent fraction, introducing said isomerizationefuent into an intermediate portion of said second fractionation zone,passing overhead from said second fractionation zone an isohexaneenriched high octane number hydrocarbon product and recovering the same,withdrawing from the bottom of said second fractionation zone a loweroctane number product than the overhead product and passing a portion ofsaid product to the upper portion of said first fractionation zone asaforesaid and recovering another portion thereof.

3. A process for the isomerization of hexane in the presence of hydrogenand an isomerization catalyst comprising alumina, platinum, and combinedhalogen, which comprises introducing a normal hexane liquid stream intoan intermediate portion of a first fractionation zone while at the sametime passing a liquid phase product stream from the bottom of a secondfractionation zone to the upper portion of said first fractionationzone, passing isohexanes from an upper portion of said firstfractionation zone and introducing the same into a lower portion of saidsecond fractionation zone, withdrawing from the bottom of said firstfractionation zone a hydrocarbon fraction enriched in normal hexane andpassing said fraction to an isomerization reaction zone wherein saidfraction is contacted with hydrogen and said isomerization catalyst,said isomerization reaction zone being maintained at a temperature offrom about 300 F. to about 850 F. and at a pressure of from about 100 toabout 1000 pounds per square inch and wherein said enriched normalhexane fraction is isomerized in the presence of said catalyst andhydrogen at a liquid hourly space velocity of from about 0.1 to about 10to an equilibrium mixture of hexane hydrocarbons, introducing saidequilibrium mixture into an intermediate portion of said secondfractionation zone, passing overhead from said second fractionation zonean isohexane enriched high octane number hydrocarbon product andrecovering the same, withdrawing from the bottom of said secondfractionation zone a lower octane number product than the overheadproduct, and passing a portion of said product to the upper portion ofsaid first fractionation zone as aforesaid and recovering anotherportion thereof.

4. The process of claim 3 further characterized in that 111 the'catalyst comprises alumina, from about 0.1% to about 2%' by weightthereof of platinum, and from about 0.1% .to about 8% by weight thereofof combined halogen.

5. The process of claim 4 further characterized in that the combinedhalogen is a mixture of chlorine and fluorine in an amount of from about0.3% to about 0.7% by weight, and the isomerizaton is carried out at atemperature of from about 750 to about 850 F.

6. The process of claim 4 further characterized in that the combinedhalogen is uorne in an amount of from about 2.5 to about 4.5%V byweight, and the process is carried out at a temperature of from about500to aboutY References Cited in the le of this patent UNITED STATESPATENTS

2. A PROCESS FOR THE ISOMERIZATION OF HEXANE WHICH COMPRISES INTRODUCINGA NORMAL HEXANE LIQUID STREAM INTO AN INTERMEDIATE PORTION OF A FIRSTFRACTION ZONE WHILE AT THE SAME TIME PASSING A LIQUID PHASE PRODUCTSTREAM FROM THE BOTTOM OF A SECOND FRACTIONATION ZONE TO THE UPPERSECTION OF SAID FIRST FRACTIONATION ZONE TO THE HEXANES FROM AN UPPERPORTION OF SAID FIRST FRACTIONATION ZONE AND INTRODUCING THE SAME INTOTHE LOWER PORTION OF SAID SECOND FRACTIONATION ZONE, WITHDRAWING FROMTHE BOTTOM OF SAID FIRST FRACTIONATION ZONE A HYDROCARBON FRACTIONENRICHED IN NORMAL HEXANE AND PASSING SAID FRACTION TO AN ISOMERIZATIONREACTION ZONE WHEREIN SAID FRACTION IS CONTACTED WITH HYDROGEN AND ANISOMERIZATION